The present invention relates to a slight-incontinence sanitary napkin structure.
As is known, the so-called SAP or superabsorbent polymer, is a polymeric material designed and suitable for absorbing great amounts of fluids and to hold them under comparatively low pressures, thereby this material is very useful for making absorbing structures or constructions for incontinence sanitary products.
The above polymer and the absorbing products obtained thereby, have been already disclosed in prior U.S. patents, such as U.S. Pat. No. 3,669,103 to Harper and U.S. Pat. No. 3,670,731 to Harmon.
The absorption capability and efficiency of SAP in disposable absorbing products greatly depend on the shapes, positions and manners by which SAP is embedded in the end product.
In some cases, i.e. as the SAP density is a comparatively high one, its efficiency may be negatively affected by the so-called gel-blocking phenomenon, which term means a condition which is achieved as the SAP is in a wet condition, and inflates and prevents liquids from arriving at inner parts of the absorbing products.
In actual practice, the fluid absorption occurs with an absorption rate much lower than the fluid releasing rate from the human body, thereby causing excessive fluid losses, without fully saturating the absorbing article SAP material, said gel-blocking phenomenon increasing as the SAP density increases.
On the other hand, a high SAP concentration would be very desirable to achieve a sufficient absorbing capability of the absorbing article or product.
Several attempts to improve the fluid absorbing efficiency of SAP materials, by reducing the above gel-blocking phenomena, are extensively disclosed in the literature.
For example, Weisman and Goldman (EP-122042), disclose an absorbing structure wherein SAP is dispersed through a hydrophilic fiber airlaid layer, compressed to set density.
Buttherworth (U.S. Pat. No. 4,235,237) discloses an absorbing article including absorbing material particles spaced from one another within the article structure.
Mazurak (EP-0063331) discloses an absorbing article containing a mixture of SAP and a filling material processed by a surface active agent.
Further prior documents disclose the arrangement of SAP materials within different absorbing article.
The EP-122042 patent discloses that a SAP containing layer may be arranged at the bottom of an absorbing article having its top part contacting the human body and comprising hydrophilic fibers only.
The U.S. Pat. No. 4,333,463 and U.S. Pat. No. 4,333,462 to Holtman disclose an absorbing article containing an amount of superabsorbing particles arranged near an end portion of the absorbing article.
Further attempts for improving SAP materials to limit the mentioned gel-blocking phenomenon have been further made and disclosed in yet other prior documents, and are mainly based on methods for allowing SAP to hold a spherical shape in a wet condition, that is to leave interstitial free spaces or cells allowing fluids to enter the core of the absorbing article.
The PCT application WO2004/096303 to Frank and Qin discloses polymers having an improved strength under a pressure condition and holding a set spherical shape, for making improved absorbing articles.
It should be pointed out that, to achieve an optimum performance in slight incontinence sanitary articles, it would be necessary to consider a further very important parameter, in addition to the article absorbing capability, that is the article body fluid absorbing rate.
In fact, an urine jet of a slightly incontinent person corresponds to a small urine amount, but with a comparatively high flow rate, since an urine loss is an event in which the incontinent person temporarily loses his/her control, typical for example because of a sneezing, laughing or an physical effort.
Thus, in slight-incontinence articles, the article absorbing rate or speed is much more important than the absorbing capability.
An increase of the absorbing capability, even if always desirable, would not be sufficient, per se, to provide a good urine absorbing performance.
Several methods for increasing the urine or fluid absorbing rate, without reducing the amount of superabsorbing polymer and holding a high absorbing power are always known, in which multi-layer structures including absorbing cores made of cellulose fibers in which the superabsorbing polymer is embedded are used.
In these structures the liquid is conveyed through the article by capillarity, the cellulose fibers operating as a vehicle to arrive at the superabsorbing polymer.
As stated, the gel-blocking phenomenon negatively affects the capillarity liquid spreading.
To overcome the above limitation, an approach would be that of using an additional absorbing layer added to the so-called “spreading or absorbing” pad, as disclosed by Pleniak in the EP-108637 patent.
Generally, this absorbing layer would comprise processed cellulose fibers, as disclosed by Cook in the PCT Patent Application WO91/11165, or a non woven fabric material, as disclosed, for example, by Palumbo and Carlucci in the PCT Patent Application WO9428838 and by Richards in the U.S. Pat. No. 5,607,414, in which no superabsorbing polymer or very small amount thereof is used.
Waksmundzki discloses in his PCT Patent Application WO2006/039307, superabsorbing polymer multilayer fluid absorbing articles.
With reference to FIG. 1 a conventional absorbing pad structure is herein shown comprising a liquid receiving layer 1, devoid of superabsorbing polymers, for quickly drawing and spreading the liquid, and an underlying pad layer 2 including a superabsorbing polymer, is arranged between two sheet elements, of which a first sheet element 3 is permeable to the liquids and contacts the body of the user and the second sheet element 4, impermeable to the fluids, faces the user garments.
Thus, in this prior structure the first layer has only a liquid drawing and non absorbing function, with the drawback that it remains wet and contacts the user skin, thereby irritating it.
A further desirable characteristic of an absorbing article, also very important for the liquid absorbing power thereof, is that of holding an integral condition with the article in a wet condition.
This may be achieved as follows:
(a) binding with one another the fibers of the absorbing layer by chemical or mechanical methods, which methods, however, make the absorbing pad much more hard thereby reducing the user comfort;
(b) using fibers of a greater average length and so braided or entangled to form a very firm or solid fiber network.
Cotton, which has very long fibers, is very suitable to form the above braided and strong constructions.
However, cotton is scarcely broadly used in absorbing products because of its high cost, larger than that of a wood cellulose fiber.
Typical absorbing structures of a cotton material could be made by overlapping multiple layers of textile fiber webs, from a carding process and blowing or suction methods, and then pressing said layers to increase the fiber cohesion, thereby the made article will comprise “combed” fibers oriented in the article longitudinal direction, and which will preferably convey the fluid through a X-Y plane and not in a depth direction.